> Viruses are the enigma of evolution. Are they just chemicals, or living?

Biology is full of edge cases like this. For a few more examples, google "species problem". Human beings often like to classify things into discrete groups, but that doesn't necessarily map onto the natural world all that well.

indeed. This reminds me of the arguments about whether fungus is a plant or an animal.

Are you sure that's a real question? The answer is probably just that the words you're using don't quite fit the underlying reality.

Natural selection mostly selects against change. Without selection the cockroach would have mutated.

Viruses are not an enigma, another parasitic genetic element are Inteins - https://en.wikipedia.org/wiki/Intein.

Viruses are not living, because they have no metabolism and they cannot self-replicate (they require the replication apparatus of the host)

Viruses are not self-contained systems, they are more like organelles of cells, which transfer data between hosts.

edit: sorry I didn't been organelles I meant vesicles in cells

This seems to me like saying "wow, that frame of film on that movie sure is lucky to be up there right now" 24 times a second.

> Still most of the species that ever lived are extinct today.

Depends on your view of the Ship of Theseus.

We wouldn't be able to mate with Nakalipithecus nakayamai, so they are indeed a distinct species despite being our ancestor.

By this criterion, there are very, very few bacterial species.

I seem to recall this being the reason the sexual reproduction definition of species is considered problematic. It's a convenient definition for animals but breaks down for most other things, and even the animal kingdom has some funky edge cases, like the https://en.wikipedia.org/wiki/Zebroid.

Or rather, each bacterium is its own species?

Why? Bacteria exchange DNA with each other.